Refrigerator liner structures

ABSTRACT

A refrigerator cabinet is provided with a plastic liner, the inside wall of the refrigerator, which is resistant to chemical degradation by fluorocarbons. Freon and Freon substitutes used as blowing agents for foaming the insulation contained between the outer metal cabinet and the inside wall of the refrigerator can cause blistering, cracking, and sometimes dissolution of materials used to form the plastic liner, which is the inside wall of the refrigerator. There is now provided a plastic liner which is resistant to those blowing agents and particularly to those blowing agents which are partially halogenated and tend to be more aggressive than Freon. The plastic liner wall maintains impact strength and toughness after exposure to fluorohydrocarbons conventionally employed in refrigerator units for in situ polyurethane foam production.

FIELD OF THE INVENTION

The invention relates to a refrigerator cabinet appliance, the liner wall of which is resistant to attack by Freon and Freon substitutes.

BACKGROUND OF THE INVENTION

Typical refrigerator appliance cabinets consist of an outer metal cabinet, an inner plastic liner, typically ABS (acrylonitrile-butadiene styrene) or HIPS (high impact polystyrene), and an insulating foam core, typically polyurethane foam. Blowing agents for the polyurethane foam are locked into the foam. Freon, a completely halogenated methane, fluorotrichloro methane, is presently employed commercially as the blowing agent. For environmental reasons, implemented by regulations, substitutes for Freon must be found. Proposed substitutes for Freon are halogenated hydrocarbons which contain at least one hydrogen atom.

Polyurethane blowing agents, such as Freon (CFC-11) and Freon substitutes, such as 2-fluoro-2,2 dichloroethane and 2,2-dichloro-1, 1,1-trifluoroethane,(HCFC 141b and HCFC 123, respectively), can cause liner blistering, catastrophic cracks, tiny cracks (crazing) and loss of impact properties (embrittlement), as well as stress whitening and/or dissolution. The blowing agents HCFC 141b and HCFC 123 appear to be more chemically aggressive than Freon (CFC-11) in attacking the liner. It is the common belief that blowing agent attack of the liner occurs on condensation of the blowing agent to liquid, which occurs on cooling. Cooling and condensation of the blowing agent does occur during shipping and storage. Shipping conditions are simulated during fabrication by cycling the appliance cabinet from hot to cold to cause evaporation and condensation of the blowing agent(s).

It is proposed to provide a plastic sheet structure to be thermoformed into a refrigeration liner that is resistant to chemical attack.

It is an object of the invention to provide a refrigeration appliance liner to be fabricated from a thermoformable, plastic sheet material exhibiting resistance to chemical attack (blistering, cracking, crazing, as mentioned above, by polyurethane foam blown with Freon (CFC-11) or potential Freon substitutes including HCFC-123 and HCFC-141b, which are mentioned above.

It is an object of the invention to provide a refrigeration appliance liner to be fabricated from a thermoformable, plastic sheet material which retains a high level of toughness (impact properties) and strength (tensile properties), even at low temperatures (at 5° F. or less).

It is another object of the invention to provide a liner made from a plastic sheet material that maintains processability similar to HIPS or ABS, including favorable extrusion conditions and similar thermoforming behavior.

It is another object of the invention to provide a liner made from a plastic sheet containing a layer of a special multi-functional blend that exhibits excellent chemical resistance to Freon or potential Freon substitutes, may additionally function as an adhesive layer between optional layers of HIPS (or ABS) and polyolefin, and finally acts as a compatibilizing agent when regrind plastic sheet scrap is recycled to virgin plastics resin being extruded into the core sheet layer.

SUMMARY OF THE INVENTION

In accordance with the invention, a refrigerator appliance is provided with a plastic liner which is substantially chemically inert to Freon and Freon substitutes. A conventional refrigerator appliance cabinet includes an outer metal cabinet, an inner plastic liner comprising ABS (acrylonitrile-butadiene styrene) or HIPS (high impact polystyrene), and an insulating foam core, typically polyurethane foam. Blowing agent for the polyurethane foam is locked into the foam.

The plastic liner serves as the inner plastic wall of the refrigerator. The plastic wall is of variable thickness, as a result of thermoforming during fabrication. However, it is formed of a composite of relatively uniform thickness.

In accordance with the invention, the plastic liner comprises a barrier layer, which is substantially chemically inert to completely halogenated and partially halogenated hydrocarbons, e.g., chlorinated and/or fluorinated hydrocarbons used as blowing agents for polyurethane foam formation. In one embodiment of the invention, a core layer of ABS (acrylonitrile-butadiene-styrene) or HIPS (high impact polystyrene), for example by coextrusion or lamination, is affixed to the barrier layer. For visual attractiveness, a glossy patina on the barrier layer or the core layer may be present either due to the inherent properties of the core layer or by providing an independent layer of material which provides high gloss.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic drawing of a refrigerator cabinet.

FIG. 2 is a schematic drawing of the plastic liner serving as plastic wall of the refrigerator.

FIG. 3 is a fragmentary cross section of the composite forming the plastic liner.

DETAILED DESCRIPTION OF THE INVENTION

The invention will be explained with reference to the appended drawings.

The refrigerator appliance, of FIG. 1, includes a cabinet and is defined by an outer cabinet metal wall 1, and inner liner wall 2, and a body of foamed-in-place insulation 3 there between. In one popular design, the cabinet may define a freezer space 4 and an above-freezing refrigeration space 5.

Inner liner wall 2 is thermoformed into the desired configuration, as shown in FIG. 2. Inner liner wall 2 is a thermoformed product of liner sheet 6, one embodiment of which is illustrated in FIG. 3 as a multi lamina composite. After being thermoformed into the desired configuration, the inner liner wall 2 is disposed into the outer cabinet wall 1 in a nested, spaced relationship for introduction of the foamed insulation by a conventional foaming in place operation. Usually the outer cabinet wall 1 and the inner liner wall 2 are joined physically by mating of joints.

The barrier layer of the invention is substantially chemically inert to halogenated hydrocarbon(s) used as blowing agents in polyurethane foam production. If a core layer is employed, it is disposed on a surface of the core layer. During polyurethane in situ foam production, in one embodiment of the invention, it is the surface of the barrier layer of the composite which is contiguous to and bonds with the foam. However, it is not essential that the barrier layer of the invention be contiguous to the foam. In FIG. 3 the barrier layer is illustrated as numeral 8.

The barrier layer comprises 4 to 50% by weight of a composite which includes a core layer and comprises polymers or copolymers of ethylene or propylene which are selected from the group consisting of polypropylene, low density polyethylene, linear low density polyethylene, high density polyethylene (melt index of 1 to 10 and density of 0.935 to 0.960), high molecular weight high density polyethylene (melt index of 0.05 to 1.0), ethylene vinyl alcohol, certain high impact polystyrenes, nylon 66, and PVC. The barrier layer may comprise one or more lamina of the same or different polymer or copolymer.

The barrier layer may, and preferably does, contain 4 to 30 weight percent of synthetic block copolymer rubber. The synthetic block copolymer rubber can be selected from styrene-butadiene diblock; styrene-ethylene/butylene-styrene triblock; styrene-ethylene/butylene-styrene triblock functionalized with maleic anhydride, maleic acid or admixtures thereof, or combinations of any of the above.

The liner sheet may be formed of ABS (acrylonitrile-butadiene-styrene) or HIPS (high impact polystyrene) core layer which constitutes the major proportion of the composite. The core layer comprises 50 to 96 weight percent of the composite. Those core materials are chemically degradable by the completely or partially halogenated hydrocarbon blowing agent, used in the polyurethane foam production. Both of these core materials are commercially available. In FIG. 3 the core layer, chemically degradable by the fluorinated hydrocarbon, is designated as 7.

The core layer which is (1) high impact polystyrene or (2) acrylonitrile-butadiene-styrene copolymer, contains 5 to 35, preferably 5 to 20, and usually 5 to 15 weight percent rubber in the form of particles. The rubber is usually polybutadiene and can be a styrene-butadiene copolymer. The rubber particles can have average diameters of at least 5 microns, and generally of at least 6 microns average diameters and up to 10 microns. When the rubber particles are 1 micron or less, as described in U.S. Pat. No. 4,513,120 high gloss polystyrene (medium impact) is produced. U.S. Pat. No. 4,513,120 is incorporated by reference herein.

Various alternatives are available for maximizing the adhesion of the core material to the barrier layer. Moreover, these alternatives can improve adhesion of the foam insulation to the barrier material. The core layer may be subjected to corona discharge treatment, or to ultraviolet light exposure, and by methods known in the art. In accordance with one embodiment of the invention, maximizing the adhesion of the the barrier layer to the foam and optionally to a core layer appears to be achieved chemically. In a preferred embodiment the material of the barrier layer contains maleic anhydride, maleic acid, and/or derivatives of maleic acid in an amount ranging from 0.1 to 10 weight percent of the barrier material. Conveniently, this can be achieved by inclusion of styrene-ethylene/butylene-styrene triblock functionalized with maleic anhydride, maleic acid or admixtures thereof; the triblock material is available from Shell Chemical Company as Kraton FG-1901X.

In one embodiment of the invention, the composite is formed with a barrier layer disposed on one surface of the core layer with a third layer of medium impact high gloss polystyrene on the exposed surface of the core layer. The third layer of medium impact high gloss polystyrene comprises 0.5 to 8 weight percent of the composite. The third layer is depicted in FIG. 3 as element 9.

The composite is formed by the coextrusion of the materials of the laminae described above. The composite sheet can then be cut into suitable lengths for thermoforming into any desired configuration, one of which is illustrated by FIG. 2. The resulting liner wall 2 is then assembled with the outer cabinet wall 1 and in situ foaming of the insulation material is performed. The resulting structure exhibits impact strength, and substantial elimination of thermal cracking and of blistering.

In situ foaming involves admixing an isocyanate with a masterbatch. The masterbatch comprises 60 to 70 percent of a polyol; 0.3 to 1.5 percent of a surfactant; 0.5 to 3.0 percent of a catalyst 0.4 to 2.5 percent of water and 12 to 30 percent of the blowing agent. The isocyanates used in applicances include TDI and PMDI. TDI comprises an 80:20 mixture of 2,4 and 2,6 isomers of products produced by dinitration of toluene, catalytic hydrogenation to the diamines, and phosgenation. Cf. Kirk Othmer, ENCYCLOPEDIA OF CHEMICAL TECHNOLOGY, Vol. 23, page 581 (Third Edition). PMDI is the reaction product formed by nitration of benzene and reduction to produce aniline; reacting aniline with formaldehyde in the presence of hydrochloric acid to produce a mixture of oligomeric amines, which are phosgenated to yield PMDI. Cf. Kirk Othmer, ENCYCLOPEDIA OF CHEMICAL TECHNOLOGY, Vol. 23, page 581 (Third Edition). The blowing agent can be Freon or Freon substitutes which are partially halogenated lower hydrocarbon of 1 to 5 carbon atoms, usually of 2 to 4 carbon atoms; halogenated includes fluorinated and/or chlorinated. By "partially halogenated" is meant that the Freon substitutes of the invention preferably contains at least one hydrogen atom. Illustrative of the partially halogenated lower hydrocarbon are 1,1-dichloro-1-fluoroethane and 2,2-dichloro-1,1,1-trifluoroethane, chlorodifluoromethane (HCFC 22); 1,1,1,2-tetrafluoro-2-chloro-ethane (HCFC 124); 1,1,1,2-tetrafluoroethane (HFC 134a) and pentafluoroethane (HFC 125). The foams produced contain in their cellular structure residual amounts of the blowing agent. The foam is formed in situ by foaming in a high pressure mixhead equipped to a nozzle for introducing the foam and foaming components into the cavity formed by the nesting of outer metal cabinet 1 and the plastic liner.

EXAMPLES Examples 1

Plastic sheets of composition described in the Table 1 were fabricated into test plaques (15"×15"×0.050") and Brett-type test panels (783/4"×7 7/8"×0.050"). These test sheets were then positioned as pairs into closed foaming jigs with a 2" space between the sheets. Polyurethane foam chemicals were then introduced into the jigs to fill the space between the plastic sheets, to produce plastic/foam/plastic composite structures. These composite structures were thermally cycled several times between -20° F. and 140° F., to cause condensation and vaporization of liquid blowing agent along the exposed plastic sheet surfaces.

Several blowing agents (CFC-11, and HCFC-123,) at several levels (9-15%) were evaluated in separate tests. CFC-11 is trichlorofluoromethane (CCl₃ F): HCFC-123 is 2,2dichloro-1,1,1,-trifluoroethane, HCFC-141b is 1,1-dichloro-1-fluroethane (CHCl₂ CF₃);

The thermally cycled composite structures were then tested, as summarized in Table 1, and inspected for signs of chemical attack.

                                      TABLE 1                                      __________________________________________________________________________     POLYSTYRENE/POLYOLEFIN BLENDS                                                  MIS-ESCR AND PHYSICAL PROPERTIES                                               __________________________________________________________________________                   MOBIL                                                                          PS7100                                                                              BLEND 1                                                                               BLEND 2                                                                               BLEND 3                                                                               BLEND 4                                                                               BLEND 5 BLEND                   __________________________________________________________________________                                                            6                       Composition (%)                                                                HIPS/PS, %    100  80     80     80     80     80      80                      Polyolefin, % 0    10     10     10     10     10      10                      Compatibilizer, %                                                                            0    10     10     10     10     10      10                      HIPS/PS, Type 7100 7100   7100   7100          7100    7100                    Polyolefin, Type   Hilmont                                                                               Aristech                                                                              Himont Mobil  Mobil   Himont                                     6231   FF-028N                                                                               SA-747M                                                                               HMA-045                                                                               MMA-169 SA-747M                 Compatibilizer, Type                                                                              Homo PP                                                                               Homo PP                                                                               Rand PP                                                                               HDPE   LLDPE   Rand PP                                    G1657  G1657  G1657  G1657  G1657   50:50                                      S-EB-S S-EB-S S-EB-S S-EB-S S-EB-S  1657:1901               MIS-ESCR, 1000 psi (min)                                                       Chiffon       63   138    394    125    63     2       600                     COOA          115  441    1186   491    256    4       5963                    CFC-11        9    7      9      8      6      0       12                      HCFC-123      5    4      14     10     2      0       14                      HCFC-141b     6    8      13     10     6      0       17                      MIS-ESCR, 400 psi (min)                                                        CFC-11        22                 37                                            HCFC-123      13                 65                                            HCFC-141b     23                 51                                            Physical Properties:                                                           MFI (G), g/10 min                                                                            2.9  9.3    6.8    8.2    8.7    12.1    5.8                     Vicat, C      103  103    103    101    100    92      101                     Tensile Yield, psi                                                                           2500 2200   2500   2100   2100   1600    2600                    Tensile Fail, psi                                                                            3500 2200   2500   2100   2100   1600    2600                    Tensile Modulus, psi                                                                         182,000                                                                             97,000 109,000                                                                               99,000 96,000 58,000  112,000                 Elongation, % 41   31     41     31     29     28      40                      Izod Impact, ft.lb/in                                                                        2.1C 1.0C   1.4C   1.2C   1.1C   1.1C    1.5C                    Gardner Impact, in.lb                                                                        123  49     95     69     18     6       93                      __________________________________________________________________________                        BLEND 7                                                                               BLEND 8                                                                               BLEND 9                                                                               BLEND 10                                                                              BLEND 11                                                                               BLEND                   __________________________________________________________________________                                                            12                      Composition (%)                                                                HIPS/PS, %         80     85     80     80     70      60                      Polyolefin, %      10     10     10     10     20      30                      Compatibilizer, %  10     10     10     10     10      10                      HIPS/PS, Type      7100   7100   7100   7100   7100    7100                    Polyolefin, Type   Himont Hilmont                                                                               Himont OxyChem                                                                               OxyChem OxyChem                                    SA-747M                                                                               SA-747M                                                                               SA-747M                                                                               L5005  L5005   L5005                                      Rand PP                                                                               Rand PP                                                                               Rand PP                                                                               HMW-HDPE                                                                              HMW-HDPE                                                                               HMW-HDPE                Compatibilizer, Type                                                                              FG1901X                                                                               G1702  G1702  FG1901X                                                                               FG1901X FG1901X                                    SEBS/MA                                                                               S-EP   S-EP   SEBS/MA                                                                               SEBS/MA SEBS/MA                 MIS-ESCR, 1000 psi (min)                                                       Chiffon            630    147    90     342    753     1700                    COOA               1708   7026   4995                                          CFC-11             14     7      5      8      13      25                      HCFC-123           20     4      3                                             HCFC-141b          18     5      4                                             MIS-ESCR, 400 psi (min)                                                        CFC-11             44                   41     48      80                      HCFC-123           69                   56     74      142                     HCFC-141b          60                   48     63      115                     Physical Properties:                                                           MFI (G), g/10 min  5.7    2.8    2.7    3.5    2.9     2.2                     Vicat, C           101    101    101    100    101     102                     Tensile Yield, psi 2800   2400   2400   3000   3070    3020                    Tensile Fail, psi  2800   2400   2400   3000   3070    3020                    Tensile Modulus, psi                                                                              116,000                                                                               152,000                                                                               145,000                                                                               138,000                                                                               130,000 124,000                 Elongation, %      40     12     7      50     46      36                      Izod Impact, ft.lb/in                                                                             1.6H   2.1C   2.1C   2.1C   2.0C    1.8C                    Gardner Impact, in.lb                                                                             99     66     66     121    127     109                     __________________________________________________________________________                        BLEND 13                                                                              BLEND 14                                                                              BLEND 15                                                                              BLEND 16                                                                              BLEND 17                                                                               BLEND                   __________________________________________________________________________                                                            18                      Composition (%)                                                                HIPS/PS, %         50     60     60     60     60      60                      Polyolefin, %      40     30     30     30     30      30                      Compatibilizer, %  10     10     10     10     10      10                      HIPS/PS, Type      7100   7100   7100   7100   7100    7100                    Polyolefin, Type   OxyChem                                                                               OxyChem                                                                               Himont Himont Chevron Chevron                                    L5005  L5005  SA-747M                                                                               SA-747M                                                                               PE5280T PE5280T                                    HMW-HDPE                                                                              HMW-HDPE                                                                              Rand PP                                                                               Rand PP                                                                               PE/EVA 8%                                                                              PE/EVA 8%               Compatibilizer, Type                                                                              FG1901X                                                                               G1657  G1657  FG1901X                                                                               FG1901X G1657                                      SEBS/MA                                                                               S-EB-S S-EB-S SEBS/MA                                                                               SEBS/MA S-EB-S                  MIS-ESCR, 1000 psi (min)                                                       Chiffon            2887   37     22     914    >10000                          COOA                                           (400 psi)                       CFC-11             31     3      4      16                                     HCFC-123                                                                       HCFC-141b                                                                      MIS-ESCR, 400 psi (min)                                                        CFC-11             130    51     48     88     75      68                      HCFC-123           270    93     146    230    150     160                     HCFC-141b          218    73     88     159    105     103                     Physical Properties:                                                           MFI (G), g/10 min  1.8    3.6    11.1   6.3    4.6     6.1                     Vicat, C           103    99     101    103    88      77                      Tensile Yield, psi 2940   2500   2200   2790   2520    2000                    Tensile Fail, psi  2940   2500   2040   2770   2520    2000                    Tensile Modulus, psi                                                                              118,000                                                                               106,000                                                                               79,000 101,000                                                                               84,000  65,000                  Elongation, %      33     34     39     36     54      42                      Izod Impact, ft.lb/in                                                                             1.5H   1.4C   1.0C   1.4C   2.6H    2.1H                    Gardner Impact, in.lb                                                                             55     100    136    154    242     215                     __________________________________________________________________________                        BLEND 19                                                                              BLEND 20                                                                              BLEND 21                                                                              BLEND 22                                                                              BLEND 23                                                                               BLEND                   __________________________________________________________________________                                                            24                      Composition (%)                                                                HIPS/PS, %         60     50     50     40     40      60                      Polyolefin, %      30     40     40     50     50      30                      Compatibilizer, %  10     10     10     10     10      10                      HIPS/PS, Type      7100   9524   7800   7800   1800    1800                    Polyolefin, Type   Chevron                                                                               OxyChem                                                                               OxyChem                                                                               OxyChem                                                                               OxyChem Mobil                                      PE5272 L5005  L5005  L5005  L5005   HYA-301                                    PE/EVA 4%                                                                             HMW-HDPE                                                                              HMW-HDPE                                                                              HMW-HDPE                                                                              HMW-HDPE                                                                               HDPE                    Compatibilizer, Type                                                                              G1657  G1657  G1657  FG1901X                                                                               FG1901X FG1901X                                    S-EB-S S-EB-S S-EB-S SEBS/MA                                                                               SEBS/MA SEBS/MA                 MIS-ESCR, 1000 psi (min)                                                       Chiffon                   >1000  >1000  >1000  >1000   223                     COOA                      (400 psi)                                                                             (400 psi)                                     CFC-11                                                                         HCFC-123                                                                       HCFC-141b                                                                      MIS-ESCR, 400 psi (min)                                                        CFC-11             53     96     88     311    346     62                      HCFC-123           126    197    170    642    627     76                      HCFC-141b          74     135    108    >1000  495     87                      Physical Properties:                                                           MFI (G), g/10 min  7.7    1.9    1.7    1.8    1.6     4.7                     Vicat, C           103    104    104    106    109     106                     Tensile Yield, psi 1930   2500   2500   2790   3890    5160                    Tensile Fail, psi  1930   2000   2300   2830   3460    5160                    Tensile Modulus, psi                                                                              61,000 102,000                                                                               103,000                                                                               122,000                                                                               174,000 229,000                 Elongation, %      42     46     48     82     23      5                       Izod Impact, ft.lb/in                                                                             1.9H   1.9C   1.7C   1.7C   0.8C    1.1H                    Gardner Impact, in.lb                                                                             240    104    89     67     14      38                      __________________________________________________________________________                               BLEND 25                                                                              BLEND 26                                                                              BLEND 27                                                                              BLEND 28                                                                               BLEND                   __________________________________________________________________________                                                            29                                   Composition (%)                                                                HIPS/PS, %   60     60     50     0       20                                   Polyolefin, %                                                                               30     30     40     80      65                                   Compatibilizer, %                                                                           10     10     10     20      15                                   HIPS/PS, Type                                                                               1800   7800   7100   7100    7100                                 Polyolefin, Type                                                                            Mobil  OxyChem                                                                               Mobil  Mobil   Mobil                                             HCX-002                                                                               L5005  HMX-034                                                                               HMX-034 HMX-034                                           HDPE   HMW-HDPE                                                                              HDPE   HDPE    HDPE                                 Compatibilizer, Type                                                                        FG1901X                                                                               FG1901X                                                                               FG1901X                                                                               FG1901X FG1901X                                           SEBS/MA                                                                               SEBS/MA                                                                               SEBS/MA                                                                               SEBS/MA SEBS/MA                              MIS-ESCR, 1000 psi (min)                                                       Chiffon      >1000  734    >1000  >1000   >1000                                COOA                                                                           CFC-11                                                                         HCFC-123                                                                       HCFC-141b                                                                      MIS-ESCR, 400 psi (min)                                                        CFC-11       679    83     351    >1000   >1000                                HCFC-123     523    120    630    >1000   >1000                                HCFC-141b    496    97     544    >1000   >1000                                Physical Properties:                                                           MFI (G), g/10 min                                                                           9.4    3.7    9.3    9.8     10.8                                 Vicat, C     103    103    105    115     108                                  Tensile Yield, psi                                                                          4140   2950   2890   1830    2170                                 Tensile Fail, psi                                                                           4140   2950   2890   1830    2170                                 Tensile Modulus, psi                                                                        192,000                                                                               151,000                                                                               126,000                                                                               58,000  71,000                               Elongation, %                                                                               15     121    18     500     477                                  Izod Impact, ft.lb/in                                                                       0.7H   4.3H   0.6C   13.8    1.4C                                 Gardner Impact, in.lb                                                                       44     207    48     >320    294                     __________________________________________________________________________      *high impact polystyrene                                                       **polystyrene                                                            

Example 2

Sheets of several different compositions described in Table 2 invention were exposed to the liquid blowing agents by sealing a glass ball joint to the sheet samples and adding the specific liquid blowing agent being evaluated (CFC-11, HCFC-123, and HCFC-141b).

The samples were exposed to the blowing agents for thirty minutes each, then exposed to heat (60° C. for 30 minutes) to drive off the blowing agents, and finally inspected for chemical attack. Several sheet samples displayed no signs of chemical attack at all, and most samples showed at least some reduction in chemical attack when compared to sheets of HIPS or ABS. The results are set forth in Table 2.

                  TABLE 2                                                          ______________________________________                                         LIQUID BLOWING AGENT CONTACT STUDY                                                       CFC-11   HCFC-123   HCFC-141b                                        ______________________________________                                         UNMODIFIED                                                                     RESINS:                                                                        Mobil PS7100 HIPS                                                                          Severe     Severe     Severe                                                   Blistering Blistering Blistering                                   Mobil PS7800 MIPS                                                                          Severe     Severe     Severe                                                   Blistering Blistering Blistering                                   Mobil PS5350 HIPS                                                                          Severe     Severe     Severe                                                   Blistering Blistering Blistering                                   Dow 469 HIPS                                                                               Severe     Severe     Severe                                                   Blistering Blistering Blistering                                   Monsanto ABS                                                                               Unaffected Cracking   Cracking                                                            Severe     No Blistering                                                       Blistering                                              PS/POLYOLEFIN                                                                  BLENDS COEX.                                                                   ON PS7100:                                                                     CA10 (10% Ran-                                                                             Severe     Severe     Severe                                       dom PP)     Blistering Blistering Blistering                                   CB30 (30% Ran-                                                                             Moderate   Moderate   Moderate                                     dom PP)     Blistering Blistering Blistering                                   LB40 (40% HMW-                                                                             Skin       Skin       Skin                                         HDPE)       Delamination                                                                              Delamination                                                                              Delamination                                             Moderate   No Blistering                                                                             No Blistering                                            Blistering                                                         BASF KR2773 Skin       Slim       Skin                                         (30% HDPE)  Delamination                                                                              Delamination                                                                              Delamination                                 (10% CaCO.sub.3                                                                            No         Slight     Slight                                       filled)     Blistering Blistering Blistering                                   BASF KR2774 Severe     Moderate   Moderate                                     (30% LDPE)  Blistering Blistering Blistering                                   BARRIER FILMS                                                                  LAMINATED ON                                                                   PS7100:                                                                        Mobil MMA-169                                                                              Moderate   Unaffected Unaffected                                   LLDPE (2 mil)                                                                              Blistering                                                         Mobil HMA-045                                                                              Unaffected Unaffected Unaffected                                   HDPE (2 mil)                                                                   Oxy L5005 HMW-                                                                             Unaffected Unaffected Unaffected                                   HDPE (2 mil)                                                                   DuPont EVOH Unaffected Unaffected Unaffected                                   (5 mil)                                                                        ______________________________________                                    

Example 3

The invention is illustrated by use in a top mount (freezer on top) refrigerator at 15 ft³ capacity, with HCFC-123 as the polyurethane blowing agent at an estimated 18% level weight.

The layers of the composite are described below.

    ______________________________________                                         Pre-Thermoformed Sheet:                                                        ______________________________________                                         Sheet Total Thickness                                                                           202 mil (0.202")                                              Barrier Layer Thickness                                                                         10 mil (0.010")                                               Core Layer Thickness                                                                            190 mil (0.190")                                              Gloss Layer Thickness                                                                           2 mil (0.002")                                                Barrier Layer % of                                                                              5%                                                            Total sheet                                                                    Pre-Thermoformed Sheet                                                                          (77.75 × 46.75 ×                                  Dimensions       0.202) inches                                                 Barrier Layer Material*                                                        Core Layer Material                                                                             Mobil ES7100 Refrigeration                                                     Grade HIPS                                                    Gloss Layer Material                                                                            Mobil ES7800 Medium Impact,                                                    High Gloss PS                                                 ______________________________________                                         *Barrier Material used had the following:                                      High Density     Mobil HMX-034 HDPE                                            Polyethylene Type                                                                               (Melt Flow = 4.0, Density =                                                    0.954)                                                        Rubber Type      Shell Chemical Co. Kraton                                                      FG-1901X                                                                       Styrene-Ethylene/Butylene-                                                     Styrene Tri-block                                                              (functionalized with 2%                                                        maleic anhydride)                                             with                                                                           Polyethylene Level                                                                              80%,                                                          Rubber Level     20%, and                                                      Irganox 1010 Antioxidant                                                                        500 ppm                                                  

The barrier layer material was compounded in a Werner & Pfleiderer ZSK30 mm twin screw extruder, at a temperature profile which ranged from 225° to 400° F.

The composite was formed from a two-layer system including the core layer (ES7100) and the barrier layer, which were coextruded. The gloss layer of medium impact polystyrene (Mobil ES7800) was laminated thereto. The temperature profile for coextrusion is set forth below:

    ______________________________________                                         Coextrusion Temperature Profile:                                               ______________________________________                                         ES 7100 Extruder                                                                             Profile (345-380-350-300-390-400)° F.                                   Die 415° F.                                                             Melt Temp 440° F.                                         Barrier Material                                                                             Profile (275-300-325-330)° F.                             Extruder      Die 415° F.                                                             Melt Temp 340° F.                                         ______________________________________                                    

The thermoformed product assembled in a metal cabinet with subsequent in situ insulation formation was subjected to 12 temperature cycles ranging from -40° F. to +150° F. Polyurethane foam adhesion to the barrier layer was good and better than the adhesion of barrier layer to the core material. The liner wall exhibited satisfactory impact strength, no signs of cracking during thermal blistering and de minimis blistering.

Example 4

A 22 ft³ refrigerator, a side-by-side model (configuration of refrigerator and freezer compartments) was fitted with a liner and then insulated with polyurethane foam produced by CFC-11 blowing agent at an estimated 16 weight % level.

The compositions, and dimensions, of the preformed sheet components are described below.

    ______________________________________                                         Sheet Total Thickness                                                                            198 mil (0.198")                                             Barrier Layer Thickness                                                                          6 mil (0.006")                                               Glue/Compat. Layer Thickness                                                                     2 mil (0.002")                                               Core Layer Thickness                                                                             188 mil (0.188")                                             Gloss Layer Thickness                                                                            2 mil (0.002")                                               Glue + Barrier Layers                                                                            5%                                                           % of sheet                                                                     Pre-Thermoformed Sheet                                                                           (78.75 × 36.00 ×                                 Dimensions        0.198) inches                                                Barrier Layer Material*                                                                          Mobil HMX-034 HDPE                                           Glue/Compatibilizer Layer**                                                                      Mobil Developmental LB40                                     Core Layer Material                                                                              Mobil ES7100 Refrigeration                                                     Grade HIPS                                                   Gloss Layer Material                                                                             Mobil ES7800 Medium Impact,                                                    High Gloss PS                                                ______________________________________                                         *Barrier Layer-Material used                                                                     Mobil HMX-034 HDPE                                                             (High Density Polyethylene)                                                    (Melt Flow = 4.0, Density =                                                    0.954)                                                       **Glue/Compat Layer Composition:                                               Polyethylene Type OxyChem Alathon L5005                                                          HMW-HDPE (Melt Flow =                                                          0.055                                                                          Cond. F, Density = 0.95)                                     Rubber Type       Shell Chemical Co. Kraton                                                      FG-1901X                                                                       Styrene-Ethylene/Butylene-                                                     Styrene Tri-block                                                              (functionalized with 2%                                                        maleic anhydride)                                            HIPS Type         Mobil ES7100 Refrigeration                                                     Grade (Melt Flow = 2.5)                                      Polyethylene Level                                                                               40%                                                          Rubber Level      10%                                                          HIPS Level        50%                                                     

The glue/compatabilizer layer materials were compounded in a Werner Pfleiderer 30 mm twin screw extruder at a temperature profile ranging from 225° F. to 450° F. The ES7800 gloss layer was laminated to the remaining laminate which were coextruded in a Welex Coextrusion System.

The unit (s) were subjected 12 times to a temperature cycle of -40 ° to 150° F. The unit exhibited satisfactory impact strength, and de minimis blistering.

Thus it is apparent that there has been provided in accordance with the invention, a refrigerator plastic liner wall that fully satisfies the objects, aims, and advantages set forth above. While the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art in light of the foregoing description. Accordingly, it is intended to embrace all such alternatives, modifications, and variations as fall within the spirit and broad scope of the appended claims. 

What is claimed is:
 1. A refrigerator appliance cabinet which comprises an outer metal cabinet and an inner plastic liner, the improvement comprising a plastic liner molded from a thermoformable composite which comprises:a core layer which is (1) high impact polystyrene or (2) acrylonitrilebutadient-styrene copolymer, said core layer containing 5 to 35 weight percent rubber in the form of particles having average diameters of at least 5 microns, said core layer having two surfaces; wherein the core layer comprises at least 50 weight percent of the composite, a gloss patina on a first of said two surfaces, a barrier material on a second of said two surfaces of said core layer, said barrier material comprising a polymer or copolymer of ethylene or propylene containing 0 to 40% of a block copolymer rubber, based upon the weight of the barrier material, said barrier material comprising 4 to 50% by weight of the composite.
 2. The refrigerator appliance cabinet of claim 1, wherein the barrier material contains maleic acid, and/or derivatives of maleic acid in an amount ranging from 0.5 to 10 weight percent of the barrier material.
 3. The refrigerator appliance cabinet of claim 1, wherein the polymer of copolymer of ethylene or propylene is selected from the group consisting of polypropylene, low density polyethylene, linear low density polyethylene, high density polyethylene, high molecular weight high density polyethylene.
 4. The refrigerator appliance cabinet of claim 3, wherein the rubber is styrene-butadiene diblock; styrene-ethylene/butylene-styrene triblock; styrene-ethylene/butylene-styrene triblock functionalized with maleic anhydride, maleic acid or admixtures thereof.
 5. The refrigerator appliance cabinet of claim 4, wherein the barrier material contains maleic anhydride, maleic acid, and/ or derivatives of maleic acid in an amount ranging from 0.5 to 10 weight percent of the barrier material.
 6. The refrigerator appliance cabinet of claim 5, wherein the gloss patina is provided by a layer of medium impact, high gloss polystyrene comprising 0.5 to 8 weight percent of the composite.
 7. The refrigerator appliance cabinet of claim 6, wherein the core layer comprises 50 to 96 weight percent of said composite.
 8. The refrigerator appliance cabinet of claim 7, wherein the core layer comprises at least 55 weight percent of said composite.
 9. The refrigerator appliance cabinet of claim 8, wherein the barrier material comprises high density polyethylene.
 10. The refrigerator appliance cabinet of claim 9, wherein the barrier material further includes at least 5 weight percent of said block copolymer rubber based on the weight of the barrier material.
 11. The refrigerator appliance cabinet of claim 10, wherein the rubber is functionalized with maleic anhydride, maleic acid or derivatives of maleic acid.
 12. A refrigerator appliance cabinet which comprises an outer metal cabinet, an inner plastic liner, and a polyurethane foam disposed between said outer metal cabinet and liner, wherein said foam contains a fluorinated hydrocarbon blowing agent and said liner is chemically degradable by the fluorinated hydrocarbon blowing agent, the improvement comprising:a plastic liner molded from a thermoformable composite which comprises a core layer which is (1) high impact polystyrene or (2) acrylonitrilebutadiene-styrene copolymer, said core layer containing 5 to 35 weight percent rubber, based on the weight of the core layer, in the form of particles having average diameters of at least 5 microns, said core layer having two surfaces; wherein the core layer comprises at least 50 weight percent of the composite, a gloss patina on a first of said two surfaces, which comprises less than 10 weight percent of the composite; a barrier material on a second of said two surfaces of said core layer, said barrier material comprising a polymer or copolymer of ethylene or propylene containing 0 to 40 weight percent of a block copolymer rubber, based on the weight of the barrier material, said barrier material comprising 4 to 50% by weight of the composite and is selected from the group consisting of polypropylene, low density polyethylene, linear low density polyethylene, high density polyethylene, high molecular weight high density polyethylene.
 13. The refrigerator appliance cabinet of claim 12, wherein the barrier material contains maleic acid, and/or derivatives of maleic acid in an amount ranging from 0.5 to 10 weight percent of the barrier material.
 14. The refrigerator appliance cabinet of claim 12, wherein the rubber is styrene-butadiene diblock; styrene-ethylene/butylene-styrene triblock; styrene-ethylene/butylene-styrene triblock functionalized with maleic anhydride, maleic acid or admixtures thereof.
 15. The refrigerator appliance cabinet of claim 14, wherein the barrier material contains maleic acid, and/or derivatives of maleic acid in an amount ranging from 0.5 to 10 weight percent of the barrier material.
 16. The refrigerator appliance cabinet of claim 15, wherein the patina comprises a layer of medium impact, high gloss polystyrene comprising 0.5 to 8 weight percent of the composite.
 17. The refrigerator appliance cabinet of claim 16, wherein the barrier material comprises high density polyethylene.
 18. The refrigerator appliance cabinet of claim 17, wherein the barrier material further includes at least 5 weight percent of said block copolymer rubber based on the weight of the barrier material.
 19. The refrigerator appliance cabinet of claim 18, wherein the rubber is functionalized with maleic acid or derivatives of maleic acid.
 20. A thermoformable composite comprising a core layer which is (1) high impact polystyrene or (2) acrylonitrile-butadiene-styrene copolymer, said core layer containing 5 to 35 weight percent rubber, based on the weight of the core layer, in the form of particles having average diameters of at least 5 microns, said core layer having two surfaces;wherein the core layer comprises at least 50 weight percent of the composite, a high gloss layer on one of said two surfaces comprising less than 10 weight percent of the composite; a barrier material on said core layer, said barrier material comprises a polymer or copolymer of ethylene or propylene containing 0 to 40% of a block copolymer rubber, said barrier material comprising 4 to 50% by weight of the composite.
 21. The composite of claim 20, wherein the the barrier material contains maleic acid, and/ or derivatives of maleic acid in an amount ranging from 0.5 to 10 weight percent of the barrier material.
 22. The composite of claim 20, wherein the polymer or copolymer of ethylene or propylene is selected from the group consisting of polypropylene, low density polyethylene, linear low density polyethylene, high density polyethylene, high molecular weight high density polyethylene.
 23. The composite of claim 22, wherein the rubber is styrene-butadiene diblock; styrene-ethylene/butylene-styrene triblock; styrene-ethylene/butylene-styrene triblock functionalized with maleic anhydride, maleic acid or admixtures thereof.
 24. The composite of claim 23, wherein the barrier material contains maleic anhydride maleic acid, and/or derivatives of either maleic acid or maleic anhydride in an amount ranging from 0.5 to 10 weight percent of the barrier material.
 25. The composite of claim 24, wherein the high gloss layer is medium impact, high gloss polystyrene, and wherein the high gloss layer comprises 0.5 to 8 weight percent of the composite.
 26. The composite of claim 25, wherein the core layer comprises at least 30weight percent of said composite.
 27. The composite of claim 26, wherein the core layer comprises 50 to 96 weight percent of said composite.
 28. The composite of claim 27, wherein the barrier material comprises high density polyethylene.
 29. The composite of claim 28, wherein the barrier material further includes at least 5 weight percent of said block copolymer rubber based on the weight of the barrier material.
 30. The composite of claim 29, wherein the rubber is functionalized with maleic acid or derivatives of maleic acid. 